Gas shield,non-consumable-electrode pulse arc welding



Nov. 3,1970 7 s, BR EIAL 3,538,301 GAS SHIELD, NON-CONSUMABLE-ELECTRODE PULSE ARC WELDING, I

Filed March 10, 1967 FIG. 1

TIG Torch DC, Power Currenr Supply Power S pp y FIG. 2

Pulsed Current Power Supply' INVENTORS ROBERT S. BRAY LUIS J. LOZANO WWM M44.

AT ORNEYS United States Patent U.S. Cl. 219-137 Claims ABSTRACT OF THE DISCLOSURE In arc welding the abutting edges of two brass strips, two power sources are used in conjunction with nonconsumable electrodes shielded by an inert-gas atmosphere. One power source principally supplies a DC, straight polarity, background current sufficient to maintain an are between the electrode and the work; the second power source, connected in parallel with the first, supplies a superimposed, pulsed DC. current sufficient to fuse the metal and effect the weld. The joint consists of a series of overlapping beads which appear on both the observe and the reverse surfaces of the weld as a series of regularlyspaced ripples.

BACKGROUND OF THE INVENTION Field of the invention This invention relates to arc welding, and, more particularly, to gas shielded, non-consumable-electrode arc welding using a combination of a DC. current and a pulsed current in the welding process.

Description of the prior art The inert-gas-shielded, metal-arc (MIG) welding process is well known and has many commercial applications. The high welding current required to transfer the consumable electrode to the work, in the MIG welding, however, limits its application and generally is not suitable for welding many heat-sensitive and reactive metals, such as brass. MIG welding, unless it is well controlled, oftentimes causes overheating in these metals which leads to a high porosity weld and in the case of brass, zinc burnout.

To minimize the overheating problems, a non-consumable electrode is substituted in the MIG welding. The process using tungsten as a non-consumable-electrode is known as TIG welding process. T-IG welding, because of its lower power requirement, creates smaller weld are heat affected zones thus eliminating the problems of excess porosity and zinc burnout in the weld. TIG welding process, however, has its drawbacks. Notable among them are slow welding speed, arc instability, and limited ranges in which the welding can be successfully carried out without either burnthrough or insuflicient penetration.

SUMMARY OF THE INVENTION We have now found that the deficiencies in the conventional TIG welding can be substantially overcome by using a dual power supply system for the welding process. Broadly stated, the method of this invention for are welding workpiece elements with a non-consumable electrode in a gas shielded atmosphere comprises applying simultaneously a direct-current and a pulsed welding current at a potential suflicient to establish an are between the workpiece elements and the electrode. The pulsed welding current has a repeated frequency in the range between and 240 per second and the direct-current is equivalent to 15% to 85% of the combined current for welding.

The weld thus obtained is a plurality of overlapping weld beads appearing as a series of uniform ripples along the weld on one surface of the work. Each weld bead 3,538,301 Patented Nov. 3, 1970 ice penetrates the work to form a second series of uniform ripples.

In the welding process of this invention, it is noted that a more stable arc condition is obtained so that a low current arc can be readily used for very light gage material. Also, higher welding speeds, exceeding three times the speed of a conventional TIG welding process are possible, the speed being related proportionally to the frequency of the high current-density pulses. In addition, a wider range of current can be used without causing burnthrough at the higher range and insufficient penetration at the lower range.

The pulsed current applied thereto generates a pulsating are which leads to the formation of a series of overlapping puddles during welding as contrasted to the conventional TIG welding process which carries a puddle along with the electrode to form a continuous weld. The overlapping weld of this invention has a narrower heat affected zone and results in less zinc burnout in welding brass. The weld has uniform penetration and, after it has been cold worked and annealed, is not noticeable (there are no apparent differences in the structure).

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a schematic diagram showing an apparatus suitable for carrying out the welding process of this invention. As illustrated, the source of the pulsed current feeds the welding arc in parallel with a DC. source for the background current supply required to maintain the arc. The DC. source can be a generator or a transformer rectifier set with a suitable series impedance to control the background current,

FIG. 2 is a diagram of a simple system for pulsed current supply which consists of a rectifier in a bridge circuit connected to an AC. welding transformer and a switching device to change from full wave to half wave.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In carrying out the process of this invention, the dual power sources are connected in parallel to a conventional TIG welding apparatus as illustrated in FIG. 1. The tungsten electrodes suitable for the welding process are available commercially and come in different sizes, for example, 35 and The diameter of the electrode selected affects the amount of the current that can be used. In general, the larger the diameter, the higher the total current it can handle.

The suitable inert gas for the welding process is helium or argon, or a mixture of these two gases. It is noted that there is less zine burnout with 70-30 brass when argon is used as a shielding gas while helium shielding produces a smoother bead surface.

Further to illustrate this invention specific examples are described hereinbelow with reference to the drawings. In these examples, 70-30 brass strips of various thickness were welded using theapparatus shown in FIGS. 1 and 2. The shielding gases and the welding conditions are specified in the examples.

EXAMPLE I 0.020" 70-30 brass strips were welded at a speed ranging from inches per minute (7.5 feet per minute) to 45 feet per minute. Welds made at 7.5 f.p.m. were performed under the following range of conditions:

TABLE I Background D.C. current2830 amp. Pulsed D.C. current55-65 amp. Total curent-8385 amp.

/2 Wave 60 c.p.s.

In order to determine optimum welding speeds, a fixture was mounted on a rotating welding positioner. Beadon-plate and butt test welds were made in the shape of 7" arcs with radii of about 12 /2". Table II lists the results of the bead-on-plate tests made at these higher speeds.

4 welding current is a one-half wave rectified alternating current.

4. A method according to claim 1 wherein the background direct and pulsed welding currents are applied in parallel to the work elements and the electrode.

1 TABLE II Background Pulse Total Speed current, current, current, Electrode Electrode travel, Amount of amp. amp. amp. Size, in. gap, in. f.p.m. penetration Number 9. 40 105 145 3/32 0. 031 24 Full.

b 40 160 200 3/32 0. 031 30 c 55 255 310 3/32 0. 02s 45 The speed of 45 f.p.m. was considered to be the prac- 5. A method according to claim 1 wherein the work tical limit for a half wave pulse cycle at 60 c.p.s. At piece elements are thin cupreous strips having zinc therein. speeds greater than 45 f.p.m. the individual pulsed welds 6. A method of arc welding thin strips with a non-condid not overlap sufiiciently. Higher speed is obtained using sumable electrode in a gas shielded atmosphere which higher frequency. A practical frequency range is between comprises applying to the strips and said electrode a back- 60 to 120 c.p.s. The process of this invention is capable ground direct-current at a potential suflicient to maintain of welding at a speed above 70 f.p.m. at 120 c.p.s. Higher an arc, simultaneously applying a pulsed current having a welding speeds would be possible with higher pulse frefrequency in the range between 15 and 240 pulses per secquencies. 0nd to the strips and said electrode in parallel relation to Pulse welded specimens were rolled in three passes with said background direct-current to supply power for weldtwo intermediate anneals from 0.020 down to 0.005. ing, and moving said electrode with respect to said strips This was done in order to assess the effect of the rougher at a rate up to about 70 feet per minute thereby depositbead surface on the finished surface of the strip. The ing on said strips a plurality of overlapping weld beads welded strip was thoroughly cleaned before each pass to form a series of uniform ripples along the weld on one through the rolls. The surface resulting was completely surface of the work. free of defects. 7. A method according to claim 6 wherein the back- EXAMPLE II ground direct-current is equivalent to 15% to 85% of the total welding current. In this p thick, 70*30 brass ps 11/8" 8. A method according to claim 6 wherein said pulsed wide were welded using the following conditions welding current is a one-half wave rectified alternating current. TABLE III 9. A method for welding thin brass strips having a Range of currents to produce acceptable 1 0 1 thickness below about 0.03 inch with a tungsten electrode amp total in a gas shielded atmosphere which comprises applying no background Cun ent 20 amp 40 background direct-current to said electrode and brass Pu1s6d D'Q current 49 61 amp strips at a potentlal sufficient to maintain an arc therebe- Arc tween, simultaneously applying a pulsed current having a Tungsten electrode 2% thoriated vertex angle--25 frequency between to 60 P111565 P minute to Said Speed of trave1 90 imp trode and brass strips to supply power for welding, said Gas shielding torch arg0n 20 f lbackground direct-current bemg equivalent to 15%-85% Gas Shielding backup he1ium -2 f h of the combined current of the direct and pulsed currents, v and moving said electrode with respect to said strips at a We claim: rate between 7.5 to 70 feet per minute whereby a plurality 1. A method of arc welding workpiece elements with a of overlapping weld beads are produced to form a series non-consumable electrode in a gas shielded atmosphere of if i l along th ld on id Strip which comprises applying to the work elements and said 10 A method according to claim 9 wherein the gas electrode simultaneously a background direct-current and shielding is argon, helium, or a mixture of these two a pulsed Welding current at a potential sufiicient to esgases, and the pulsed current is a one-half wave rectified tablish an are, said pulsed welding current having a frealternating current. quency in the range between 15 and 240 pulses per second and said background direct-current being equivalent to References Cited 15% to 85% of the total welding current and moving the UNITED STATES PATENTS electrode relative to the workpiece elements at rate whereby a plurality of overlapping weld beads are deposited on 3,339 8/1967 A1denhfi 219 131 X the workpiece elements to form a series of uniform rip- 3390250 6/1968 Apbletyt et a1 219 196 ples along the weld on one surface of the work.

2. A method according to claim 1 wherein the back JOSEPH TRUHE Pnmary Exammer ground direct-current is applied to maintain the arc dur- J. G. SMITH, Assistant Examiner ing welding and said pulsed D.C. welding current is applied to supply the power necessary for welding. 6

3. A method according to claim 1 wherein said pulsed 8222 33 UNITED STATIIS PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3, 0 Dated November 3. 1970 Inventor(s) Robert A. Bray et al.

It is certified that error appears in the above-identified patent and that. said Letters Patent are hereby corrected as shown below:

Column 1, line 22, "observe" should read -ob\ Ierse Column 2, line 7l, "cureut" should read -current- Column 3, lines 13 and 14, should read '--full Column 3, line 57, "at rate" should readr-a rate-- Column 4, line 59, "196" 'should read 1963-- $5GNB mg:

' EQLED 

